Unseptquadium
Unseptquadium, Usq, is the temporary name for element 174. NUCLEAR At least one set of theoretical values for half-lives and decay modes of Usq have been constructed for neutron count up to N = 333(1). It predicts isotopes ranging from Usq 469 to Usq 506 in two bands: Usq 469 to Usq 493 and Usq 503 to Usq 506. Examination of pp 15 & 18 of Ref. 1 indicates that Usq 469 through Usq 493 are part of the expected pattern of alpha-decaying nuclei centered on the N = 308 shell closure. The band Usq 480 to Usq 482 are predicted to decay by alpha emission with sub-millisecond half-lives, while the remainder of the band mainly show the expected sub-microsecond half-lives. Usq 484 and Usq 485 are indicated to have half-lives up to 1 sec and to decay by positron emission. Neutron counts for the isotopes involved are 310 <= N <= 312, which implies alpha decay and a shorter half life. Those nuclei are more likely to be similar to the other isotopes in their band. What Ref. 1 can’t do is describe heavy isotopes of Usq. It is possible to use a first-order, liquid-drop approach to guess at what lies there. At least two computations of the neutron dripline’s location up to Z = 175 exist(2),(3), and since they give similar results, the maximum possible size of a Usq nucleus can be set slightly above the values computed, allowing only a small margin for error. This gives Usq 622 as the heaviest possible Usq isotope. Similarly, a realistic lower bound can be set by requiring that the amount of energy needed to stabilize a nucleus be no more than twice what is needed to stabilize Usp 471. Within this range, the liquid-drop model can be used to indicate the amount of structural correction energy needed to allow a drop of nuclear matter to survive for the 10^-14 sec needed for electromagnetic interactions (such as binding an electron) to become important. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(3),(4), 370(3), 318(5), and 308(1). The isotope Usq 580 requires 1.5 MeV of structural correction, which means isotopes in the Usq 570 to Usq 585 band are likely. (See “Formation” for additional significance of these nuclei.) Usq 544 requires 2 MeV of structural correction, which means isotopes in the band Usq 534 to Usq 549 are also likely. All isotopes in both bands should beta-decay with half-lives under a second. On the other hand, Usq 492 requires 6.5 MeV of correction energy, which means it can only stabilize nuclides if it provides strong correction. Ref. 1 does not show a pattern of nuclides which indicate strong closure at N = 318. Usq 482 requires 8.5 MeV of correction energy, which is realistic for a strong neutron shell closure, such as the one predicted at N = 308, so the liquid-drop picture isn’t unrealistic. ATOMIC Electron structure of Usq has not been studied closely, but it is likely to differ significantly from the conventional orbitals found in lower-Z nuclei. While only the innermost electrons would be qualitatively different, other electrons are likely to be quantitatively different from those in lower-Z atoms. Usq is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Usq to have different electronic structures. Predictions of atomic or chemical properties of Usq are risky. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Usq 570 to Usq 577 to form in quantity during such a merger. It improbable that nuclides between Usq 534 and Usq 549, or lighter, can form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Usq 469 to Usq 493 band. Quantities produced by this method are very small. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 3. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 4. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-11-19)